feat: implement wiki-linked categories with graph and backlinks integration

Add complete category system that integrates with Obsidian's wiki-linked
category frontmatter. Categories appear as pills on pages and link directly
to category notes (not aggregation pages).

Features:
- Parse [[Page Name]] syntax from category frontmatter
- Display category pills styled like tags
- Link directly to category notes
- Integrate with graph view connections
- Enable bidirectional backlinks
- Preserve case in category slugs

Implementation:
- Added extractWikiLinks() to frontmatter transformer
- Created CategoryList component for pill rendering
- Modified links transformer to include categories in links array
- Updated contentIndex to export category metadata
- Added i18n strings for category UI elements
- Set includeEmptyFiles: true to show empty category pages in graph

Files modified:
- quartz/plugins/transformers/frontmatter.ts
- quartz/plugins/transformers/links.ts
- quartz/plugins/emitters/contentIndex.tsx
- quartz/components/CategoryList.tsx (new)
- quartz/components/pages/CategoryContent.tsx (new)
- quartz/plugins/emitters/categoryPage.tsx (new)
- quartz/i18n/locales/en-US.ts
- quartz/i18n/locales/definition.ts
- quartz/components/index.ts
- quartz.layout.ts
- quartz.config.ts
- README.md (updated with Quartz updater documentation)

Security: Comprehensive privacy review confirms NO information leaks from
private folder. All ignore patterns working correctly.

Docs: Added CUSTOMIZATIONS.md with complete feature documentation,
implementation details, and privacy audit results.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

quartz/components/index.ts

@@ -1,5 +1,6 @@
 import Content from "./pages/Content"
 import TagContent from "./pages/TagContent"
+import CategoryContent from "./pages/CategoryContent"
 import FolderContent from "./pages/FolderContent"
 import NotFound from "./pages/404"
 import ArticleTitle from "./ArticleTitle"
@@ -12,6 +13,7 @@ import Spacer from "./Spacer"
 import TableOfContents from "./TableOfContents"
 import Explorer from "./Explorer"
 import TagList from "./TagList"
+import CategoryList from "./CategoryList"
 import Graph from "./Graph"
 import Backlinks from "./Backlinks"
 import Search from "./Search"
@@ -28,6 +30,7 @@ export {
   ArticleTitle,
   Content,
   TagContent,
+  CategoryContent,
   FolderContent,
   Darkmode,
   ReaderMode,
@@ -38,6 +41,7 @@ export {
   TableOfContents,
   Explorer,
   TagList,
+  CategoryList,
   Graph,
   Backlinks,
   Search,